This invention relates to a novel method for preparing a screen structure for a cathode-ray tube and particularly, but not exclusively, to a novel method for preparing a light-absorbing matrix for a color-television-picture tube.
Color-television-picture tubes which include a light-absorbing matrix as a structural part of the luminescent viewing screen have been described previously, for example, in U.S. Pat. Nos. 2,842,697 to F. J. Bingley and 3,146,368 to J. P. Fiore et al. These patents describe color-television-picture tubes of the aperture-mask type (also called shadow-mask type) in which a light-absorbing matrix is located on the inner surface of the faceplate of the tube. The matrix has a multiplicity of openings therein, which may be in the shape of dots or lines, with phosphor filling each opening in the matrix.
A reverse-printing method for preparing a light-absorbing matrix for a cathode-ray tube is described in U.S. Pat. No. 3,358,310 issued Jan. 26, 1971 to E. E. Mayaud. In a preferred embodiment of that method, the inner surface of the faceplate of a cathode-ray tube is coated with a film of clear water-based photosensitive material, typically a dichromate-sensitized polyvinyl alcohol. A light image is projected on the film to insolubilize selected regions of the film. The film is flushed with water to remove the still-soluble regions of the film while retaining the insolubilized regions in place. Then, the developed film is overcoated with a layer containing particles of screen structure material, such as graphite. Finally, the retained film regions are removed together with the overlying overcoating, while retaining those portions of the overcoating in the regions previously occupied by removed still-soluble portions of the film. Such a process produces satisfactory screen structures, although further improvements in the process are desirable, for example, by providing shorter exposure times for the film and better definition of the structure.